S S symmetry Article Engineering Graphics for Thermal Assessment: 3D Thermal Data Visualisation Based on Infrared Thermography, GIS and 3D Point Cloud Processing Software Daniel Antón 1,2 and José-Lázaro Amaro-Mellado 3,4,* 1 Research Group ‘TEP970: Innovación Tecnológica, Sistemas de Modelado 3D y Diagnosis Energética en Patrimonio y Edificación’, Departamento de Expresión Gráfica e Ingeniería en la Edificación, Escuela Técnica Superior de Ingeniería de Edificación, Universidad de Sevilla, 4A Reina Mercedes Avenue, 41012 Seville, Spain; [email protected] 2 The Creative and Virtual Technologies Research Laboratory, School of Architecture, Design and the Built Environment, Nottingham Trent University, 50 Shakespeare Street, Nottingham NG1 4FQ, UK 3 Departamento de Ingeniería Gráfica, Universidad de Sevilla, 41092 Seville, Spain 4 Instituto Geográfico Nacional—Servicio Regional en Andalucía, 41013 Seville, Spain * Correspondence: [email protected] Abstract: Engineering graphics are present in the design stage, but also constitute a way to com- municate, analyse, and synthesise. In the Architecture-Engineering-Construction sector, graphical data become essential in analysing buildings and constructions throughout their lifecycles, such as in the thermal behaviour assessment of building envelopes. Scientific research has addressed the thermal image mapping onto three-dimensional (3D) models for visualisation and analysis. However, the 3D point cloud data creation of buildings’ thermal behaviour directly from rectified Citation: Antón, D.; Amaro-Mellado, infrared thermography (IRT) thermograms is yet to be investigated. Therefore, this paper develops an J.-L. Engineering Graphics for open-source software graphical method to produce 3D thermal data from IRT images for temperature Thermal Assessment: 3D Thermal visualisation and subsequent analysis. This low-cost approach uses both a geographic information Data Visualisation Based on Infrared Thermography, GIS and 3D Point system for the thermographic image rectification and the point clouds production, and 3D point Cloud Processing Software. Symmetry cloud processing software. The methodology has been proven useful to obtain, without perspective 2021, 13, 335. https://doi.org/ distortions, 3D thermograms even from non-radiometric raster images. The results also revealed 10.3390/sym13020335 that non-rectangular thermograms enable over 95% of the 3D thermal data generated from IRT against rectangular shapes (over 85%). Finally, the 3D thermal data produced allow further thermal Academic Editors: Sergei D. Odintsov behaviour assessment, including calculating the object’s heat loss and thermal transmittance for and José Rojas Sola diverse applications such as energy audits, restoration, monitoring, or product quality control. Received: 2 January 2021 Keywords: 3D thermal data; 3D thermograms; point cloud data; visualisation; temperature; heat Accepted: 16 February 2021 loss; infrared thermography; GIS; 3D point cloud processing software; engineering graphics Published: 18 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- iations. As a graphical expression, engineering graphics are useful for conceptual and project representation in the design stage, but also constitute a way to communicate, analyse and synthesise [1,2]. In the Architecture-Engineering-Construction (AEC) sector, the use of graphical data becomes essential when dealing with the analysis of the built environment, buildings and constructions throughout their lifecycles [3]. This type of data can involve the Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. use of two-dimensional (2D) and three-dimensional (3D) graphics, in the form of raster and This article is an open access article vector representations, as well as data and models based on 3D coordinates, respectively. distributed under the terms and Within this framework, several digital technologies allow the integration of additional conditions of the Creative Commons information to the graphical data, such as Geographic Information Systems (hereinafter, Attribution (CC BY) license (https:// GIS) and Building Information Modelling (henceforth, BIM) [4]. This can be useful for the creativecommons.org/licenses/by/ analysis of both geometric and geographical issues, as well as buildings and construction 4.0/). processes. In this sense, there are relevant scientific works to be highlighted dealing with the Symmetry 2021, 13, 335. https://doi.org/10.3390/sym13020335 https://www.mdpi.com/journal/symmetry Symmetry 2021, 13, 335 2 of 18 tools that support this research: Lerma et al. [5] implemented an architectonic GIS to analyse multi-source data, including thermal images, and rectified imagery; Previtali et al. [6] used a GIS-assisted method to improve the thermal anomalies recognition, mainly for thermal gradient assessment; Yuanrong et al. [7] designed a GIS to bring both Unmanned Aerial Vehicles and Terrestrial Laser Scanning data together for façade construction supervision; Chen et al. [8] used a GIS-based platform to integrate the façade data from different sources, such as infrared thermography (hereinafter, IRT), laser scanner, or high definition digital cameras; and Wang et al. [9], in the frame of digital cities, studied the semantic information on parametrised 3D buildings’ façades by hierarchical topological graphs. In the scientific literature analysed, the information associated with the geometry of the studied objects has been considered an attribute. Therefore, these attributes have not been represented as an integral part of 3D geometric data where one of the coordinates is not geometric. Concerning the rectification of images, it is worth highlighting the work by Yue et al. [10], who automatically rectified the building images helped by a local symmetry feature graph. Thus, the authors matched both the original and the corrected image in order to conduct their fusion. Finally, Soycan and Soycan [11] revised the models to achieve rectified photographs for further façades analysis. Regarding the use of 2D graphical data for building analysis, IRT is a versatile, non- destructive technology that enables the recording and visualisation of the thermal radiation emitted by the bodies. This can be used to determine energy loss in building envelopes, issues in building services, construction defects, among many others [12]. Likewise, active IRT has been proven useful to detect hidden openings or structural elements [13]. The thermal image produced by IRT, called thermogram, is 2D. Still, certain proprietary software for this sort of equipment such as InfReC Analyzer [14] or Fluke SmartView [15] can complement these images with 3D graphs [16,17]. Nevertheless, the 3D data that can be produced do not represent the thermal images’ real magnitude, given the IRT survey data’s perspective distortion. Furthermore, these applications can generally be acquired together with the equipment or in a complementary manner, which entails additional investment. Scientific research has also addressed thermal image mapping onto 3D models for visualisation and analysis. Alba et al. [18] proposed a method to texture 3D building models using infrared images. Vidas et al. [19] presented a hand-held mobile system that combined a range sensor with an IRT camera to produce 3D models mapped with infrared and Red- Green-Blue colour (hereinafter, RGB) images. Wang et al. [20] developed a hybrid system integrating Light Detection And Ranging (LiDAR) technology and an infrared camera to produce thermal models of building envelopes. Borrmann et al. [21] combined 3D laser scanning, IRT, and a photo camera to map 3D building façade models. Rangel et al. [22] presented an automatic approach to creating 3D thermal models by fusing IRT images and spatial data from a depth camera. Ham and Golparvar-Fard [23] proposed a 3D thermal mesh modelling method to display the as-is condition assessment of buildings. Thus, the method permitted the visualisation of R-value distributions and potential condensation issues. Moghadam and Vidas [24] designed a hand-held 3D thermography device called ”HeatWave” that combined IRT, a range sensor and a photo camera to create 3D models with augmented temperature and visible information of the objects. Moghadam [25] also presented a hand-held 3D device for medical thermography to simultaneously show both 3D thermal and colour information to facilitate diagnosis. Matsumoto et al. [26] developed a hand-held system based on IRT and an RGB-D (RGB depth sensor) camera for 3D model and temperature change visualisation from arbitrary viewpoints via augmented reality. Nakagawa et al. [27] established a system combining IRT and an RGB-D camera for scene 3D reconstruction; later, the authors applied the Viewpoint Generative Learning method to the RGB 3D model to display the difference between the temperature of random scene viewpoints and known camera poses. Natephra et al. [28] integrated thermographic images along with air temperature and relative humidity values into BIM to create 4D models of the performance of existing building envelopes. Finally, Landmann et al. [29] presented a high-speed system based on a structured-light sensor and an infrared camera to measure Symmetry 2021, 13, 335 3 of 18 3D geometry and the fast-moving objects’ temperature. The reviewed scientific literature continues to address the problem of representing the thermal behaviour of objects by associating thermal